Along the Pacific coast of North America
sea anemones of the genus Anthopleura are
dominant intertidal coelenterates. They occur as
solitary tide pool inhabitants (A . xanthogrammica)
or as aggregations carpeting firm substrates
(A. elegantissima). One of the unique
features of these species is their invariable symbiotic
association with unicellular Dinophyceae.
These brown or yellow-brown algae, known as
zooxanthellae, occur intracellularly in the gastrodermal
tissues of the host anemone (Muscatine,
1961) .